WASHINGTON
— Under blue skies and a gentle breeze, the scene from the grassy hill overlooking the Pentagon is unsettlingly peaceful.

Largely eclipsed by the nation's emotional focus on the ground zero cleanup in New York City, the shattered Pentagon is looking like its old self. Workers hoist into place, one by one, some of the last few blocks of bisque-colored Indiana limestone  on schedule to finish this week a near-perfect replication of the military headquarters' stately 1940s façade.

But when inbound jets approach on the way to nearby Reagan National Airport, it can feel like a rolling replay of the Sept. 11 terrorist attack.

That roar above is a reminder construction manager Daniel Monte doesn't need. At 9:38 on the morning of the attack, he was outside the Pentagon's west corner when he saw American Airlines flight 77 drop down, clip two light posts, and veer left.

"At that point, I knew the plane was not going back up," Mr. Monte recalls. He ran from the building, hearing the jet engines rev just before the aircraft plowed into the Pentagon. The blast threw him to the ground. He struggled toward the grassy hill overlooking the Pentagon, as secondary explosions ripped the air and the edifice began belching black smoke and red flames from burning jet fuel.

The strike killed 125 people working in the Pentagon, in addition to 64 people aboard flight 77. It missed Monte by less than a minute. He was just leaving the building near the Naval Operations Center as a naval officer helped two women scan their cards to go in. "Those two ladies and that gentleman never left the Navy Ops," he says.

Today, Monte and hundreds of other workers are laboring around the clock on what for many has become a deeply personal mission: To fortify the entire Pentagon against future attacks  and have employees back at their desks in the outermost damaged section by 9:38 a.m. this Sept. 11.

"When that plane came in, I lost a part of me," says Monte, surveying the dusty bustle of cranes, forklifts, and hard-hatted workers. "I'm going to do everything I can to get it back."

Toiling day and night under an American flag and giant countdown clock emblazoned with "Let's Roll," workers are four weeks ahead of schedule. Last fall they demolished 400,000 square feet of damaged area in 32 days  ordinarily a six-month job. Sacrificing holidays and pitching in to overcome obstacles, they are now racing into the home stretch of the "Phoenix Project" to re-erect the Pentagon out of the ashen ruins.

"We're like a big machine working all together," says Douglas Ortiz, general manager for CPF and Potomac Services, the firm keeping the construction site clean. "We have a meeting every day at 7 a.m. If someone has a problem, others say, 'We'll take care of it.' "

The unity of purpose comes in true melting-pot style: At different phases of the project the number of immigrant workers has ranged from an estimated 25 percent to 80 percent of the 700 workers on site each day, says renovation spokesman George Jackson.

"Even though I wasn't born in this country, my kids were," says Mr. Ortiz, who arrived from El Salvador as a 17-year-old in 1989. Pointing to photos of his three young daughters taped to his hardhat, he says: "This is our home."

Yet if workers like Ortiz are renovating the Pentagon with unprecedented speed, even more important are the safety features they're putting in place to protect against future acts of terrorism.

In one bright side to the horrific 9/11 attack, the plane happened to strike the building at its strongest point  Wedge 1  the first newly fortified section to be completed under an upgrade project begun in 1998. Built during World War II, it is the world's largest low-rise office building and a National Historic Landmark  but hasn't met building code for years. Several features  such as a new sprinkler system and blast-resistant windows  helped prevent more casualties among the 2,600 people working in the area when the plane hit and exploded from the inside "similar to an armor-piercing round," in the words of Phoenix Project Manager Will Colston.

Yet engineers surveying the wreckage and interviewing survivors discovered more needed safety improvements. For example, the Pentagon's roof of slate-over-wood was "pure kindling" as Monte says, and is being replaced with slate over concrete. Corridors and stairwells are being hardened with concrete masonry units. More exit halls are being built. Floor level, photo-luminescent signs able to glow for hours will supplement overhead exit signs obscured by smoke on 9/11.

Workers realize there is no such thing as an attack-proof building, but they are determined to create a new Pentagon that is "100 percent stronger" than the old one, Monte says.

From the hill overlooking the building, rosaries, a tiny Christmas stocking, and origami cranes from New Hope, Penn. decorate a makeshift shrine. A plastic Batmobile and other mementos sit at the base of a tree next to a sign: "that those who died shall not have died in vain."